1. Field of the Invention
The present invention relates to a digital television (TV) broadcast signal receiver that can receive digital television broadcast signals such as ATSC (Advanced television systems Committee).
2. Description of the Related Art
In the North American Continent where an ATSC digital television broadcast (it is abbreviated to a hereinafter TV broadcast) is performed, plains are dotted with metropolises, so that various TV broadcast signals broadcasted in the suburbs of each metropolis can be received at other cities or the halfway point of the cities. In consideration from a user who receives the TV broadcast signals, since many TV broadcast signals are transmitted in various directions, it is necessary to regulate a direction of an antenna in an orientation to a TV broadcasting station from which a program which he wants to watch is delivered. Therefore, a multi-directional antenna such as a smart antenna is put into practical use.
With respect to an apparatus for controlling a signal receiving direction of an antenna, Publication of Japanese Patent Application No. 5-232205 shows an apparatus mounted on a moving body such as a vehicle for following a communication satellite. Publication of Japanese Patent Application No. 2003-60423 shows a smart antenna used for communicating between a mobile phone and a base station.
According to the EIA-909 technical standard, it is provided that a smart antenna has sixteen signal receiving directions in respective directions where a circle is divided into sixteen.
By the way, there are many types of the multi-directional antenna, for example, a type for rotating an antenna with a motor for switching the signal receiving direction, or a type with a plurality of antennas and electronic switches in which a signal receiving direction is switched by switching on and off of the electronic switches (the antenna itself is immovable). A term necessary for switching the signal receiving direction of the multi-directional antenna is uneven according to a configuration, specification, and so on of the multi-directional antenna. Specifically, the term necessary for rotating the effective signal receiving direction of the antenna with the motor is much longer than that for switching the effective signal receiving direction of the multi-directional antenna by switching the electronic switches. Furthermore, even in the same type of rotating an antenna with a motor, the power of the motor is different according to the specification or price of the multi-directional antenna. Thus, the rotation speed of the antenna or the term necessary for changing the effective signal receiving direction of the motor is uneven.
On the other hand, a digital TV broadcast signal receiver in compliance with the EIA-909 technical standard can switch an effective signal receiving direction of the multi-directional antenna such as the smart antenna to one of all the sixteen signal receiving directions. The digital TV broadcast signal receiver, however, has no function for distinguishing the kinds or specification of the connected multi-directional antennas. Therefore, a control signal for switching or changing the effective signal receiving direction of the multi-directional antenna is outputted from the digital TV broadcast signal receiver to the multi-directional antenna at an interval (first interval) longer than a term necessary for changing the effective signal receiving direction of the multi-directional antenna in which the rotation speed of the antenna is slowest among the ones available in the market.
In addition, there are digital TV broadcast signal receivers having an automatic scanning function for selecting a signal receiving direction of the multi-directional antenna in which a TV broadcast signal of a channel chosen by a user can be received at the best condition. In general, an antenna of a TV station, that is, a position of a TV tower is invariance. Thus, a TV broadcast signal of each channel is searched in each sixteen signal receiving direction as an initial processing of the digital TV broadcast signal receiver, and a signal receiving direction, in which the signal receiving condition is the most suitable, is set as an optimum signal receiving direction of each channel. For example, in the United States, a TV station can be established relatively easier. In contrast, a TV station suddenly becomes bankrupt. Therefore, it happens that a new channel, which cannot be received beforetime, can be received, or an old channel receivable long before cannot be received. Furthermore, a signal receiving condition of a TV broadcast signal of a channel is varied due to construction of a high-rise building. Thus, it becomes necessary to reset an optimum signal receiving direction for receiving a TV broadcast signal of a channel chosen by a user. Even when a multi-directional antenna having a shorter term necessary for switching or changing the effective signal receiving direction of the multi-directional antenna is connected to a digital TV broadcast signal receiver with automatic scanning function, the interval of outputting the control signals for switching or changing the effective signal receiving direction of the multi-directional antenna is longer. Thus, a term for switching or changing the effective signal receiving direction of the multi-directional antenna to an optimum signal receiving direction of a channel chosen by a user becomes much longer, and it causes the irritation of the user. Especially when the user reshuffles the channel frequently, the automatic scanning operation cannot catch up with the channel reshuffling operation, so that the automatic scanning is nonfunctional in practice.